A disc jockey or DJ is a person who selects and plays prerecorded music for an audience. There are several types of disc jockeys. Radio DJs introduce and play music that is broadcast on AM, FM, shortwave or digital radio stations. Club DJs select and play music in a bar, club, disco, a rave, or even a stadium. Hip hop disc jockeys select, play and create music with multiple turntables, often to back up one or more MCs. In reggae, the disc jockey (deejay) is a vocalist who raps, toasts or chats over pre-recorded rhythm tracks while the individual choosing and playing them is referred to as a selector. Mobile disc jockeys travel with portable sound systems and play at a variety of events.